1. Field of the Invention
The present invention relates to testing the sharpness of needles. In particular, the invention relates to an apparatus and method to determine the sharpness of the point of a curved surgical needle by measurement of the forces required to push the needle point through a supported membrane.
2. Description of Related Art
A point may be defined as a microscopic area forming the connecting surface to three or more macroscopic planes These planes intersect at a solid interior angle of less than 180.degree. . As the angle of intersection or as the radius of the tip of the point decreases, the tip becomes sharper and requires less force to penetrate an object or surface.
Various refinements have been made over the years in the structures of surgical needles. It is considered advantageous in the field to structure sharpness characteristics of surgical needles toward the purpose of achieving the most efficient penetrating function. This goal facilitates ease of use by the surgeon and minimizes pain and apprehension of the patient. Regardless of the innovation in structure, uniformity in the sharpness of surgical needles has been difficult to achieve. High volumes of surgical needles are used each year. Since they are mass produced, selected samples must be subjected to testing procedures.
Among known methods for determining the sharpness of a point is visual examination under a microscope. Physical examination or noting contour by touch has also been used. Major drawbacks of such testing are the lack of uniformity and reproducibility of the test results.
Needle test apparatus which are automatic in operation have been devised. However, such systems which often utilize complicated electrical and mechanical components are subject to certain drawbacks. Beside their complexity they are generally bulky and their size limits their adaptation to portable usage.
There exist pocket sized point sharpness testers which measure depth to width ratio of a test point. One drawback of these devices is that they warn the user if the sharpness of a point is greater than a predetermined ratio, but they do not produce an absolute measure. Because of this drawback, such devices have not been greatly used for testing surgical needles. Furthermore, since sharpness or dullness is being determined by geometric configuration alone, it is necessary that the point have sufficient strength and rigidity to maintain its original shape when touched.
Another method of testing the sharpness of needles involves measuring the linear displacement of a resilient support.
A major disadvantage of devices for testing curved needles is that the curvature of the needle renders it difficult to pierce a test bed with the needle in a manner that perpendicularity of the needle with respect to the test bed is maintained at all times during the test. For example, even a slight variation of the movement of the needle from the true radius thereof will cause the needle to penetrate the test bed by forces other than pure piercing forces, i.e., forces caused by movement of the body of the needle in the plane of the test bed.
To date, an apparatus and method for quantitatively and accurately testing the point sharpness of needles which utilizes a measure of perpendicular force required to push a needle point through a supported membrane at a given rate of penetration, have not yet been devised. I have invented an apparatus and method which accomplish this objective.